Story based achievement can't be missed.
Don't Go Gently
Optional objectives
Use heavy shot to incapacitate the Man O' War: 1/1
Kill guards: 4/4
Vanglorious Bastards
Optional objectives:
Damage the Royal African Pearl with an upgraded ram
Use the fort's defenses to sink a ship
MISSION NOTE: a few necessary prerequisites
It is recommended that you conquer the Cabo De Cruz Fort before approaching this mission. And if you haven't done so yet, upgrade the Jackdaw's battering ram to level 2 or higher. It will help in aiding for the optional objectives of this mission.
Marooned
Optional objectives:
Skin animals: 3/3
Air assassinate Vane